Figure 4: Effect of midkine siRNA on cytoprotection. (a) ELISA assay and (b) western blot were used to confirm decreased expression of midkine in doxorubicin resistant SK-N-SH cells (DoxR) treated with midkine. Culture medium from SK-N-SH wild type (WT), DoxR, DoxR cells treated with scramble sequence siRNA (DoxR-scramble), and DoxR cells treated with siRNA to midkine (DoxR-si-midkine) was harvested after growth for 96 hours. (c) SK-N-SH WT cells were grown in co-culture with WT, DoxR, and DoxR-scramble or DoxR-si-midkine cells. Co-cultures were incubated for 48 hours with or without doxorubicin at 10−7 M and 10−6 M. SK-N-SH WT cell survival was then quantified through cell counting after staining with trypan blue. Data represents the average of 4 experiments +/− SE. (d) OSA WT cells were grown in co-culture with OSA WT, DoxR, and DoxR-scramble or DoxR-si-midkine cells. Co-cultures were incubated for 48 hours with or without doxorubicin at 10−7 M and 10−6 M. OSA WT cell survival was then quantified through cell counting after staining with trypan blue. Data represents the average of 4 experiments +/− SE.